In the processing and packaging of semiconductor devices, wire bonding continues to be the primary method of providing electrical interconnection between two locations within a package (e.g., between a die pad of a semiconductor die and a lead of a leadframe). More specifically, using a wire bonder (also known as a wire bonding machine) wire loops are formed between respective locations to be electrically interconnected.
An exemplary conventional wire bonding sequence utilizing ball bonding includes: (1) forming a free air ball on an end of a wire extending from a bonding tool; (2) forming a first bond on a die pad of a semiconductor die using the free air ball; (3) extending a length of wire in a desired shape between the die pad and a lead of a leadframe; (4) stitch bonding the wire to the lead of the leadframe (forming a second bond); and (5) severing the wire. In forming the bonds between (a) the ends of the wire loop and (b) the bond site (e.g., a die pad, a lead, etc.) varying types of bonding energy may be used including, for example, ultrasonic energy, thermosonic energy, and thermocompressive energy, amongst others. As is known to those skilled in the art, this sequence is exemplary in nature, and the order may be changed in a given application (e.g., the first bond may be formed on the substrate, etc.).
U.S. Pat. Nos. 7,377,415 entitled “Bond Head Link Assembly for a Wire Bonding Machine”; 6,412,683 entitled “Cornercube Offset Tool”; and 6,176,414 entitled “Linkage Guided Bond Head” relate to the field of bondhead assemblies and vision systems used in connection with wire bonding operations, and are hereby incorporated by reference in their entirety.
To help ensure proper orientation of the various components throughout the wire bonding process (and, thus, to help achieve a high quality bond), it is desirable to calibrate a bondhead assembly (e.g., including a transducer and a bonding tool) by defining a “zero” parameter of the bondhead assembly and, more specifically, the substantial perpendicularity of the transducer with respect to a Z axis. Due to the substantially perpendicular relationship between the bonding tool and the transducer, defining the “zero” parameter of the bondhead assembly also generally defines the substantial perpendicularity of the bonding tool with respect to a bonding surface.
An example of a conventional calibration method for bondheads includes a manual, iterative technique that typically begins with the removal of various components of the wire bonding machine (e.g., an electronic flame-off wand, etc.). More specifically, a perpendicularity gage is placed on the bonding surface below the transducer. An operator manually manipulates the transducer in relation to the perpendicularity gage and, through the use of a Z-axis encoder, defines the “zero” parameter of the bondhead assembly. The previously removed components of the wire bonding machine are then re-installed to support a wire bonding operation. Such a manual, iterative technique (1) requires a particular level of operator skill, (2) is susceptible to human error, (3) is undesirably time consuming, and (4) adds to the cost of the wire bonding operation.
Thus, it would be desirable to provide an improved calibration apparatus and method to overcome one or more of the deficiencies of conventional calibration methods for bondheads.